READV(3P)                                           POSIX Programmer's Manual                                          READV(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       readv - read a vector

SYNOPSIS
       #include <sys/uio.h>

       ssize_t readv(int fildes, const struct iovec *iov, int iovcnt);


DESCRIPTION
       The readv() function shall be equivalent to read(), except as described below. The readv() function shall place the input
       data into the iovcnt buffers specified by the members of the iov array: iov[0], iov[1], ..., iov[ iovcnt-1].  The  iovcnt
       argument is valid if greater than 0 and less than or equal to {IOV_MAX}.

       Each  iovec  entry  specifies  the  base address and length of an area in memory where data should be placed. The readv()
       function shall always fill an area completely before proceeding to the next.

       Upon successful completion, readv() shall mark for update the st_atime field of the file.

RETURN VALUE
       Refer to read().

ERRORS
       Refer to read().

       In addition, the readv() function shall fail if:

       EINVAL The sum of the iov_len values in the iov array overflowed an ssize_t.


       The readv() function may fail if:

       EINVAL The iovcnt argument was less than or equal to 0, or greater than {IOV_MAX}.


       The following sections are informative.

EXAMPLES
   Reading Data into an Array
       The following example reads data from the file associated with the file descriptor fd into the buffers specified by  mem-
       bers of the iov array.


              #include <sys/types.h>
              #include <sys/uio.h>
              #include <unistd.h>
              ...
              ssize_t bytes_read;
              int fd;
              char buf0[20];
              char buf1[30];
              char buf2[40];
              int iovcnt;
              struct iovec iov[3];


              iov[0].iov_base = buf0;
              iov[0].iov_len = sizeof(buf0);
              iov[1].iov_base = buf1;
              iov[1].iov_len = sizeof(buf1);
              iov[2].iov_base = buf2;
              iov[2].iov_len = sizeof(buf2);
              ...
              iovcnt = sizeof(iov) / sizeof(struct iovec);


              bytes_read = readv(fd, iov, iovcnt);
              ...

APPLICATION USAGE
       None.

RATIONALE
       Refer to read().

FUTURE DIRECTIONS
       None.

SEE ALSO
       read(), writev(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/uio.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     READV(3P)